Ultra-pure, paper-thin green LEDs produced for more beautiful displays

Sep 11, 2017: Researchers from ETH Zurich have produced the “purest” green, ultra-slim, bendable LED. This would improve the colour quality in next generation ultra-high definition displays required for television and smartphones.

The results of this study—titled “Ultrapure Green Light-Emitting Diodes Using Two-Dimensional Formamidinium Perovskites: Achieving Recommendation 2020 Color Coordinates”, also attended by Wendelin Stark, ETH professor of functional materials engineering, and researchers from South Korea and Taiwan, —has been published in Nano Letters. The researchers made efforts to meet the 2020 standard requirement by producing an optimized LED device whose color gamut covers 97% and 99% of the required 2020 standard in the CIE 1931 and the CIE 1976 color space. To mention here, today’s TV displays cover on average of only 73 to 78% of these color spaces.

Chih-Jen Shih, the Professor of Technical Chemistry, who made the breakthrough, said, “Nobody else can produce such a pure green light as we can at the moment.”

In order to enable the screens to display clearer, sharper, and finely graded images in the near future, the electronic devices can produce ultra-pure red, blue and green. This is largely possible today for red and blue. In the green, on the other hand, technology has hitherto reached its limits.

The published paper details the design of colloidal two-dimensional (2D) formamidinium lead bromide (FAPbBr3) hybrid perovskites with an engineered dielectric quantum well (DQW). It shows a high exciton binding energy of 162 meV, and a photoluminescence quantum yield of about 92% in spin-coated films.

They were successful in producing a green light of 99% pure LED, together with existing red and blue light technologies. This allows a wider range of colours to be displayed, with finer hues. The pure green LED is produced at room temperature, making it possible to industrialize production through a low-cost roll-to-roll process.

The researchers explain that because the human eye can distinguish between more intermediary green hues than red or blue ones, there would always be perceivable color shortcomings due to the lack of a pure green light source.

The researchers said that they need to improve the efficiency of their materials as well as their lifespan. After that a patent will be filed, and then the device can be commercialized.

Shih’s breakthrough is not based solely on the result, but also on the material used and on the process. In fact, Shih and his staff have developed an ultra-bright and bendable light-emitting diode, which can be produced with simple processes at room temperature and emits pure green light.